Doppler miss simulator



UnitedStates atent O DoPPLER Miss srMULAToR Martin R. Richmond,Cambridge, Mass., assigner to Raytheon Manufacturing Company, Newton,Mass., a corporation of Delaware l Appiication .lune 20, 1951, SerialNo. 232,529

i v11 Claims. (Cl. `23S- 61) This invention relates to an apparatus forsimulating by an electrical analogue quantity the distance of a missilefrom a target at the closest point of approach in terms of the frequencyof oscillation of an electricalcurrent.

InV the design of guided missiles directed to their target by radar, theproblem arises of detonating the charge of such a missile -at the propermoment. This should be done when the missile is closest to the target.The rate of approach of the missile to the target will pass through zeroat the point of closest approach. This would indicate the desirabilityof detonating the charge under control of the Doppler frequencygenerated by a radar system voperated on this principle. The point atwhich the Doppler frequency-passes through Zero could be used to triggerthe detonationequipment. was found to be impractical because the antennaof the radar system could not track the. target closely enough duringthisiperiod andthe change in the Dopper fre quency could be as greatyasa million cycles per second. This would be too great forapractical'computer set to follow.

it was thusfnecessary to calculate the time to the point of closest miss(T) at some earlier time and to use this value for setting a timingmechanism whichwill operate the detonator at T :0. In the course oftesting in the laboratory equipment designed for such av system, it isnecessary to simulate the Doppler eiect that would" be obtained from aDopper radar in a missile traveling toward a target at a certainrelative velocity along a certain course. `By the present invention,this is accomplished by representing the distance between the missileand the target by a frequency varying from some maximum value to zero asdetermined by the vector sum of two voltages in quadrature phaserelationship.

Other and further advantages of this invention will be apparent as thedescription thereof progresses, reference being had to the accompanyingdrawings, wherein:

Fig. l is a diagrammatic illustration of the problem to oe simulated bythe apparatus of the invention;

Fig. 2`is a schematicdiagram of one embodiment of the invention; and

Fig. 3 is a schematic. diagram of another embodiment of. the invention.i

In Fig'. l thenumeral ,101 represents the target, in this case anairplane yingazcourse designated bythe line 11. Armissile or vehicle12isguided along a course 13 and is `shown at afpoint 14; It will beseen-thatithe shortestl distance between, the :missile'12` andthe target10 willbe measured alongthe line lit-,atr any angle to the missilecourse 13, which line 15 becomes the perpendicularkl of length m,- the.minimum distance between the missile and target whenftl'iewmissilereaches the point 17.

The missile isfassumed to have a velocity Vm along its course asrepresentedby the arrow 18. This velocity is taken as the algebraic surnof the velocity of the missile and the componentofthe velocity of thetarget projected on the 'course' of themissile; The missile is also ap'-proachiiigthe'target at a'velocityVdrepresented by the' This directsysteml ICC arrow 20. The velocity Vo becomes zero when the missilevreaches the point 17, its nearest point to the target 10. The distanceit is desired to represent by a frequency is m measured along the line16.

By the present invention, the problem shown in Fig. 1 may be representedby the electromechanical` analogue of Fig. 2 or the electronic analogueof Fig. 3. bodiment of Fig. 2 more clearly demonstrates the principle ofthe invention, but the electronic analogue lof Fig. 3 is preferable foractual use.

In the embodiment shown in Fig. 2, a source of high frequency energy 21is applied across `a potentiometer 22 and a capacitor 23 connected inseries.

It will be apparent `that taking the component of the voltage due tothe` dropacross the potentiometer 22, or

` any part of it, as a reference, the component of the voltage due tothe drop across thejcapacitor 23 will be 90 degrees'` out of phase. Thevector sum of thesevoltages appears between the arm 24 of thepotentiometer 22 and ground. The` total resistance of the potentiometer22 is proportional to the maximum range of the radar used in thelproposed control system. The voltage across the capacitor 23 isproportional to the miss distance m. The resistive component of thevoltage on thearm 24 is proportional to the distance along the lines 13from the missile 12 to the point 17. The distance along the line 15 isequal to square root of the sum of the squares of the distance mi andthe distance from the missile 12- to the point 17. in voltage thisrepresents the vector s um of the resistive and capacitive components ofthe voltage at the arm of the potentiometer 22. t l

. If the arm 24 is swept along the potentiometer 22 byv the motor 25' ata rate proportional to the velocity Vm of the missile along its course,the in-phase voltage at the arm ZY-i also varies directly at a rateproportional to the velocity Vm. The vector sum of the out-of-phase andin-` phase voltages at this point the square root of the sum of thesquares ofthe two voltages) varies at a rate proportional to thevelocity V0, the rate of change` of the distance between the missile 12and the target 10.

This voltage is rectied in a detector 26 of standard design; The outputof the detector is differentiated in the circuit comprising' a capacitor27 with a resistor` 28 shunted" across it. The output of this circuit isproportional to the velocity Vo.

This voltage is then amplified in an amplifier 30 of conventionaldesign. The output of the amplifier is'used to vary the frequency of anoscillator 31.

In a Doppler system, Zero frequencyV represents `zero speed,` andfrequency is a function of the relative speedV of the radar and thetarget. In thisk system, `the voltage atthe output of the amplifier 30is proportional to this speed. This voltage varies from a maximum valueto zero. This variation in voltage is applied to the oscillator 31 toproduce a variationinfthe frequency of its output from a maximum Valuefor maximum Voltage input and speed to zero for zero voltage input andzerospeed. Preferably the frequency produced should be directlyproportional tothe voltage applied.

Tliis'can be done in several known ways. The voltage'` maybe applied tothe control grid of a reactance tube connected across the tank circuitof theoscillator, or it may be applied to aservornotor to produce achange in the `adjustment of a tuning element of the oscillator topro-duce the desired frequency of? the output of the oscillater.

This varying frequency output may also be obtained Patented July 30,1957V .f 3 varied in amplitude from some large value to zero. This maybe done by applying thevoutput of a saw-tooth voltage generator 34having theggvave form 35 to the modulator 33 to give the output of-theoscillator 32 the modulated form 36. The wave form 35, is made to varyata rate proportional to the velocity Vm of the missile. Thus theenvelope of this modulated output 36 is made to vary at a rateproportional to the velocity Vm of the missile.

This modulated output is applied to an amplifier 37 of conventionaldesign where it is mixed with the remaining lportion of the oscillatoroutput which has passed through a 90 degree phase shifter 3S, which maybe of vany conventional design. This phase shifter 38 replaces 'thecapacitor 23 of the circuit shown in Fig. 2.

- The` output of the phase shifter is then applied to a potentiometerV40 where a portion proportional to the desired miss distance is selectedby the arm 41 and applied `to-the input of the amplifier 37. There thetwo signals, that from modulator 33 and that from the phase shifter v38,in quadrature, are mixed and the resulting signalV is subsequentlyrectified in the detector 42, which may be of a'design similar to thatof the detector 26 of Fig'. 2. Y'

"Therectified signal is applied to the differentiating circuitvcomprising a capacitor 43 and a resistor 44 similar to the circuit inFig. 2 comprising capacitor 27 and resistor 28.

This differentiatedsignal is then applied to the input of a` directcurrent amplifier 45, the output of which is used to control thefrequency of the output of a variable frequency oscillator 46 to producea frequency F proportional to the miss distance m of Fig. 1.

The output of the amplifier 45 may be utilized for this purpose in muchthe same manner as the output of the amplifier 30 of the circuit shownin Fig. 2 is used to control the oscillator 31 of that circuit. Themodulator 33 could, of course, be a motor driven potentiometer.

YIn operation, the potentiometer arm 41 is adjusted to select thedesired miss distance, and the repetition rate andslope` of thesaw-tooth wave 35 produced by the generator 34 is' adjusted to selectthe speed of the missile desiredto be represented. The result will be afrequency of the outputof the oscillator 46 proportional or equal to theDoppler frequency to be expected from a radar system used ina guidedmissile under the selected conditions'.` In the circuit of Fig. 2, thecapacitor 23 could be made variable to represent any of several desiredmiss distances, while the speed of the motor 25 could be varied torepresent the desired velocity Vm of the missile 12. The result ofeithercircuit is a laboratory instrument that is'capable of producing afrequency equal to that to be expected from a Doppler radar operating ina guided missileunder a range of conditions. Such an apparatus permitsthe laboratory study of the operation of guided missile control devicesdepending upon a Doppler frequency for their operation. The signalproduced by such an equipment varies directly as the factors that woulddetermine it in the completed control system of a guided missile. Itsuse avoids the expense and inconvenience ofco'nducting the tests with anactual guided missile.

v'This invention is'not limited to the particular details ofconstruction, materials and processes described, as many equivalentswill suggest themselves to those skilled in theart., It is accordinglydesired that the appended claims be given a broad interpretationcommensurate with the scope of the invention Within the art.

What is claimed is: Y

1. In an apparatus for producing Yoscillatory electrical energy at afrequency proportional to the relative velocity between an object and adistance measuring device, the combination of a source of oscillatoryelectrical energy, with means to control the frequency of said source inaccordance with the derivative ofthe amplitude of a varyingunidirectional voltage proportional to the vector sum of two alternatingcurrent voltages in phase quadrature relationship, a first said voltageproportional to the projection of the miss distance on the course of themissile and a second voltage proportional to the distance between thesources of the missile and the target, means for continuously varyingthe amplitude of the first of said voltages in a linear manner and meansto shift the phase of the second of said voltages degrees with respectto the first, said continuously varying means comprising a motor drivenpotentiometer and said phase shifting means comprising a capacitor. A

2. Apparatus for producing oscillatory electrical energy of a frequencyproportional to the relative velocity between an object and a distancemeasuring device, comprising a first source of oscillatory electricalenergy, a second source of oscillatory electrical energy, means toselect a portion of the output of said first source proportional to themiss distance, means to vary a second portion of the output of saidfirst source in amplitude with relation to-time in a linear manner at arepetition rate proportional to the velocity of the missile desired tobe represented, means to combine the two portions of the output of thefirst source as modified, means to rectify thei combinedfoutput,means todifferentiate the combined output, and means to utilize the resultingvarying unidirectional voltage to control the frequency of the output ofthe second source so that the frequency of this output is proportionalto the relative velocity between the object and the distance measuringdevice.

y 3. Apparatus for producing oscillatory electrical energy of afrequency proportional to the relative velocity between an object and adistance measuring device, comprising a first source of oscillatoryelectrical energy, a second source of oscillatory electrical energy,means to select' a portion of the output of said first sourceproportional to the miss distance, means vto shift this portion of theoutput in phase by ninety degrees, means to vary a second portion oftheoutput of said first source in amplitude with relation to time in alinear manner at a repetition rate.proportional to the velocity of themissileY desired to be represented, means to combine the two portions oftheoutput of the first source as modified, means to rectify the combinedoutput, means to differentiate the combined output, and means to utilizethe resulting varying unidirectional voltage to control the frequency ofthe output of the second source so that the frequency of thisoutput isproportional to the relative velocity between .the object and thedistance measuring device.

4.*Apparatus for producing oscillatory electrical energy of afrequencyproportional to the relative veloeity'betwe'en' an object and a distancemeasuring device, comprising a first source of oscillatory electricalenergy,a second source of oscillatory electrical energy, means to selecta portion of the output of said first source proportional to the missdistance, means to vary a second portion of the output of said firstsource in amplitude with relation to time in a linear manner at arepetition rate proportional to the velocity of the missile desired tobe represented comprising a modulator and associated sawtooth voltagegenerator, means to combine the two portions of the output of the firstsource as modified, means to rectify the combined output, means todifferentiate 'the Ycombined output, and means to utilize the resultingvarying unidirectional voltage to control the frequency of the output ofthe second source so that the frequency of this output is proportionalto the relative velocity between the object and the distance measuringdevice.'v

5. Apparatus for producing oscillatory electrical energy of a frequencyproportional to the relative velocity between an object and a distancemeasuring device, comprising a first source of oscillatory electricalenergy, a second source of oscillatory electrical energy, means toselect a portion of the output of said first source proportional to themiss distancemeans to vary a second portion of the output of said firstsource in amplitude with relation to time in a linear manner at arepetition rate proportional to the velocity of the missile desired tobe represented, means to combine the two portions of the output of therst source as modified in series, means to rectify the combined output,means to differentiate the combined output, and means to utilize theresulting varying unidirectional voltage to control the frequency of theoutput of the second source so that the frequency of this output isproportional to the relative velocity between the object and thedistance measuring device.

6. Apparatus for producing oscillatory electrical energy of a frequencyproportional to the relative velocity between an object and a distancemeasuring device, comprising a rst source of oscillatory electricalenergy, a second source of oscillatory electrical energy,

means to select a portion of the output of said rst source proportionalto the miss distance, means to vary a second portion of the output ofsaid first source in amplitude with relation to time in a linear mannerat a repetition rate proportional to the velocity of the missile desiredto be represented, means to combine the two portions of the output ofthe first source as modified in parallel, means to rectify the combinedoutput, means to differentiate the combined output, and means to utilizethe resulting varying unidirectional voltage to control the frequency ofthe output of the second source so that the frequency of this output isproportional to the relative velocity between the object and thedistance measuring device.

7. Apparatus for producing oscillatory electrical energy of a frequencyproportional to the relative velocity between an object and a distancemeasuring device, comprising a first source of oscillatory electricalenergy, a second source of oscillatory electrical energy, means toselect a portion of the output of said first source proportional to themiss distance, means to shift this portion of the output in phase byninety degrees, means to vary a second portion of the output of said rstsource in amplitude with relation to time in a linearV manner at arepetition rate proportional to the velocity of the missile desired tobe represented comprising a modulator and associated sawtooth voltagegenerator, means to combine the two portions of the output of the firstsource as modified, means to rectify the combined output, means todifferentiate the combined output, and means to utilize the resultingvarying unidirectional voltage to control the frequency of the output ofthe second source so that the frequency of this output is proportionalto the relative velocity between the object and the distance measuringdevice.

8. Apparatus for producing oscillatory electrical energy of a frequencyproportional to the relative velocity between an object and a distancemeasuring device, comprising a first source of oscillatory electricalenergy, a second source of oscillatory electrical energy, means toselecta portion of the output of said first source proportional to themiss distance, means to shift this portion of the output in phase byninety degrees, means to vary a second portion of the output of saidfirst source in amplitude with relation to time in a linear manner at arepetition rate proportional to the velocity of the missile desired tobe represented, means to combine the two portions of the output of therst source as modified in series, means to rectify the combined output,means to differentiate the combined output, and means to utilize theresulting varying unidirectional voltage to control the frequency of theoutput of the second source so that the frequency of this output isproportional to the relative velocity between the object and thedistance measuring device.

9. Apparatus for producing oscillatory electrical energy of a frequencyproportional to the relative velocity between an object and a distancemeasuring device, comprising a first source of oscillatory electricalenergy, a second source of oscillatory electrical energy, means toselect a portion of the output of said first source proportional to themiss distance, means to shift this portion of the output in phase byninety degrees, means to vary a second portion of the output of saidfirst source in amplitude with relation to time in a linear manner at arepetition rate proportional to the velocity of the missile desired tobe represented, means to combine the two portions of the output of thefirst source as modied in parallel, means to rectify the combinedoutput, means to differentiate the combined output, and means to utilizethe resulting varying unidirectional voltage to control the frequency ofthe output of the second source so that the frequency of this output isproportional to the relative velocity between the object and thedistance measuring device.

l0. Apparatus for producing oscillatory electrical energy of a frequencyproportional to the relative velocity between an object and a distancemeasuring device, comprising a first source of oscillatory electricalenergy, a second source of oscillatory electrical energy, means toselect a portion of the output of said rst source proportional to themiss distance, means to shift this portion of the output in phase byninety degrees, means to vary a second portion of the output of said rstsource in amplitude with relation to time in a linear manner at arepetition rate proportional to the velocity of the missile desired tobe represented comprising a modulator and associated sawtooth voltagegenerator, means to combine the two portions of the output of the firstsource as modified in series, means to rectify the combined output,means to differentiate the combined output, and means to utilize theresulting varying unidirectional voltage to control the frequency of theoutput of the second source so that the frequency of this output isproportional to the relative velocity between the object and thedistance measuring device.

1l. Apparatus for producing oscillatory electrical energy of a frequencyproportional to the relative velocity between an object and a distancemeasuring device, comprising a rst source of oscillatory electricalenergy, a second source of oscillatory electrical energy, means toselect a portion of the output of said first source proportional to themiss distance, means to shift this portion of the output in phase byninety degrees, means to vary a second portion of the output of saidfirst source in amplitude with relation to time in a linear manner at arepe- ,tition rate proportional to the velocity of the missile desiredto be represented comprising a modulator and associated sawtooth voltagegenerator, means to combine the two portions of the output of the firstsource as modified in parallel, means to rectify the combined output,means to differentiate the combined output, and means to utilize theresulting varying unidirectional voltage to control the frequency of theoutput of the second source so that the frequency of this output isproportional to the relative velocity between the object and thedistance measuring device.

References Cited in the file of this patent UNITED STATES PATENTS2,170,487 Soler Aug. 22, 1939 2,486,265 Dennis Oct. 25, 1949 2,600,264Proctor June 10, 1952

